Twelve of the injured were in critical condition, Fars said, citing Hassan Qadami, the head of Iran's Crisis-Management Headquarters.

The U.S. Geological Survey said the 5.6-magnitude quake was centered about 39 miles (63 km) northeast of the Persian Gulf city of Bushehr, where the nuclear plant is located, and 7 miles (14 km) northeast of Borazjan.

The quake struck at a relatively shallow -- and therefore more likely to be damaging -- depth of 10.2 miles (16.4 km) at 5:21 p.m. local time. A reporter for the state-run Islamic Republic News Agency in Borazjan said residential buildings were damaged and electricity was disrupted to several areas, including sections of Borazjan.

The city is in Bushehr province, which is the site of a nuclear power plant that went online in 2011. There was no immediate report of how the plant fared in Thursday's temblor.

Iranian President Hassan Rouhani said he was "deeply saddened" to hear of the casualties and expressed condolences to the victims' families.

A 6.3-magnitude earthquake in May killed 39 people and injured 850 in Bushehr province, but the reactor was not affected, it said.

Iran's semi-official Mehr News said people who were afraid of aftershocks were staying out of their homes. Rescue teams were on the scene, Mehr said, quoting the governor of Bushehr Province, Fereydoun Hassanvand.

Iran's location atop several major faults leaves it prone to earthquakes.

In August 2012, two earthquakes in northwestern Iran struck 11 minutes apart -- the first a 6.4 magnitude, and the second a 6.3 magnitude, killing at least 306 people.

In 2003, a magnitude 6.6 quake struck the city of Bam in southeast Iran, killing some 31,000 people.

A 1990 quake in the northwestern provinces of Gilan and Zanjan killed as many as 50,000.